Improvements in radial-type hydraulic machines

ABSTRACT

A radial-type hydraulic machine has a number of sets of hydraulically interconnected cylinders, each set consisting of four cylinders, and a cam with which pistons in the cylinders cooperate. The cam has a number of lobes equal to the number of sets of cylinders. Each lobe is divided in profile into two symmetrical halves, each half comprising in sequence a first circular section, a first parabolic section, a spiral section, a second parabolic section, and a second circular section. This configuration ensures that the sum of the linear speeds of those pistons which are at any instant travelling in a working stroke is constant, and in turn that the swept volume is constant throughout the operating cycle. In a motor, the torque and rotational speed are therefore constant for a constant-pressure, constant-volume supply of hydraulic fluid.

United States Patent 375,077 12/1887 Lnn IMPROVEMENTS IN RADIAL-TYPE HYDRAULIC MACHINES 5 Claims, 6 Drawing Figs.

U.S. Cl 91/491, 91/184,91/188,92/72 Int. Cl F01b l/06, FOlb 13/06, F011 21/07 Field of Search 91/184, 188,192, 72,491; 103/161 References Cited UNITED STATES PATENTS 1,730,659 10/1929 Johnson et a1. 92/72 2,198,759 4/1940 Oadet 92/72 3,344,715 10/1967 Wilson 92/72 FQREIGN PATENTS 965,618 8/1964 Great Britain... 1,129,145 9/1956 France 91/184 Primary Examiner-Paul E. Maslousky Attorney-Sughrue, Rothwell, Mion, Zinn and Macpeak ABSTRACT: A radial-type hydraulic machine has a number of sets of hydraulically interconnected cylinders, each set consisting of four cylinders, and a cam with which pistons in the cylinders cooperate T cam has a number of lobes equal to the number of sets of cylinders. Each lobe is divided in profile into two symmetrical halves, each half comprising in sequence a first circular section, a first parabolic section, a spiral section, a second parabolic section, and a second circular section. This configuration ensures that the sum of the linear speeds of those pistons which are at any instant travelling in a working stroke is constant, and in turn that the swept volume is constant throughout the operating cycle. In a motor, the torque and rotational speed are therefore constant for a constantpressure, constant-volume supply of hydraulic fluid.

)L\ 21 111 I 5 l 15 6 l l' I a I 22 10 27 4 x 3 g PATENTEU JUN 8 i971 SHEEI 1 BF 4 PATENTED JUN I 8 l97| SHEET 2 [1F 4 E Q-Z PATENTEI] JUN 8 19H SHEET 3 [1F 4 PATENTEU JUN a 19m SHEET l [1F 4 IMPROVEMENTS IN RADIAL-TYPE HYDRAULIC MACHINES This invention relates to hydraulic machines and more particularly to hydraulic motors capable of even operation at low.

rotational speeds. The invention is particularly, but not exclusively, concemed with hydraulic motors adapted for use in machine tools, for example for providing controlled movement of slides, work tables, revolving turrets and the like.

It is now general practice to employ hydraulic motors instead of electric motors to power the various operations in machine tools. Such hydraulic motors may be incorporated within a servo-controlled system and in addition to providing a high degree of evenness of operation at high speeds, exhibit rapid response and dynamic stability of operation as a result of the high ratio of their generated driving torque to the inertia of the driven mechanism.

Conventional hydraulic motors do, however, incorporate relatively movable parts which slide in frictional contact. The frictional drag between these relatively movable parts increases with a decrease in relative velocity until at low velocities the drag becomes comparable with the torque generated. Under these conditions variations in frictional drag, which inevitably occur, become significant and correspondingly modify the rotational speed of the motor. Such speed variations in the operation of such an hydraulic motor at low speeds prevent the use of a direct coupling between the motor and the driven mechanism.

This difficulty is overcome only by the provision of reduction gearing between the motor and the driven mechanism, so as to enable the motor to operate at low speeds for relatively higher motor speeds. Such gearing, however, introduces objectionable play, and increases the overall inertia of the driving system, reducing the speed of response of the system to a changing demand. Moreover, where the driven mechanism is intended to operate over a wide range of speeds as well as at low speeds, the speed of the motor at high mechanism speeds may be excessively high, particularly if a high gear ratio is employed.

It is one object of the present invention to provide a hydraulic motor providing even operation at low speeds, while avoiding these drawbacks.

More particularly, an object of the invention is to provide such an hydraulic motor which can be directly coupled to a driven mechanism, without any intermediate coupling means such as gearing.

A further object of the invention is to provide a hydraulic motor with a strictly constant rotational speed over a complete revolution, provided the motor is fed with hydraulic fluid at a strictly constant feed rate.

A further important object of the invention is to provide a hydraulic motor wherein the torque remains constant over a wide range of angular speeds for a constant hydraulic feed rate.

Further objects of the invention are the provision of a motor having a rapid response to demanded speed changes and wherein friction is minimized in order to provide even, slow rotation and high mechanical efficiency.

The invention accordingly provides a dynamo-hydraulic machine, such as an hydraulic motor, comprising: a rotatable drive shaft, a central cam secured to the drive shaft, two sets of cylinders extending radially with respect to the drive shaft, pistons arranged for axial sliding movement within the respective cylinders and cooperating with the cam, and hydraulic fluid inlet and outlet ports in said cylinders, the cam being two-lobed with a symmetrical profile having parabolic portions, whereby in operation the combined instantaneous piston speeds in each set of cylinders and the combined instantaneous hydraulic fluid flow rates are constant and equal to the maximum piston speed and maximum flow rate in one cylinder.

Preferably the cam profile includes, in each lobe, parabolic portions equaling in number the number of cylinders in each said set. Said parabolic portions are preferably interconnected by portions of circular profile concentric with the axis of rotation of the cam at the regions of maximum and minumum radius of the cam; centrally of the flanks of the cam profile the parabolic portions may be interconnected by substantially linear portions. Consequently, diagrams representing the variation of the linear speed of each piston are, in the preferred embodiment, trapezoidal.

In order to reduce friction a roller is preferably carried by each piston and is urged into contact with the cam. Each said roller is preferably supported upon a shaft and a shoe supports said shaft, a spherical joint being provided between the shoe and the piston. Transverse loads on the piston are preferably absorbed by respective fixed guides, bearings at the ends of the roller shafts running within said guides.

The invention will be more clearly understood from the following detailed description, given by way of example, with reference to the accompanying drawings, wherein:

FIG. 1 is a partial axial sectional view of an hydraulic motor according to a preferred embodiment of the invention;

FIG. 2 is a part-sectional view on line IIII of FIG. 1;

FIG. 3 is a sectional view on an enlarged scale on line III-III of FIG. 2;

FIG. 4 shows diagrammatically the hydraulic interconnections of some of the motor cylinders;

FIG. 5 is a diagram showing the variation of the linear speeds of those pistons of the motor of FIGS. 1 to 4 travelling in a working stroke during a rotation through of the motor shaft; and

FIG. 6 is a diagram showing the developed profile of a lobe of the motor cam for producing the piston speed variations of FIG. 5.

Referring to FIGS. 1 to 4, the hydraulic motor has a body I comprising two spaced parallel discs 2, 3 having interposed therebetween an annular member 4.

The annular member 4- is formed with a plurality of radial cylindrical bores each adapted to accommodate a cylindrical sleeve 5 in which a respective piston 6 is axially movable.

Each sleeve 5 is provided with annular passages or ports 7, 8, 9 and 10 connecting with tangential conduits ll, 12, I3 14 respectively, the ports being selectively closed by the piston 6 on its operative stroke. Thus the piston 6 includes, intermediate its ends, a circumferentially continuous annular groove 6a which provides intercommunication between selected ports in the sleeve as described in detail hereafter.

The pistons 6 cooperate with a central cam 15 which is keyed to a rotatable motor drive shaft 16 arranged centrally of the annular member 4 in the motor body 1.

Each piston 6 engages the cam 15 through a cam-follower roller 17, which transmits thrust to or from the cooperating piston 6 by way of a coupling comprising a shoe 18 located in the respective sleeve 5 and connected to the piston 6 by way of a spherical joint 19. The shoe 18 carries a rotatable shaft 20 to which the respective cam-follower roller 17 is keyed.

The shaft 20 is provided with freely rotatable end roller bearings 21 which roll over corresponding guide tracks 22 formed in the annular member 4. The tracks 22 absorb the lateral or transverse components of the reaction between the respective pistons 6 and the cam 15 in operation of the motor.

The motor cylinders are closed at their radially outer ends by plugs 23 provided with springs 24 acting on the pistons 6 to urge the latter radially, maintaining the respective rollers 17 in contact with the cam 15 and the respective shoes 18 in engagement with the pistons 6.

In the embodiment shown, the motor is provided with eight identical radial cylinders arranged symmetrically about the motor drive shaft 16 in two sets of four adjacent cylinders the two sets cooperating with two corresponding identical lobes on the cam 15. The two cylinder sets are hydraulically interconnected and are not differentiated from each other by any structural features.

The cam 15 has two lobes, and the cylinders of the two sets of four cylinders are symmetrically disposed about the motor drive shaft 16 and extend radially of the shaft. Each set is arranged to maintain the overall swept volume of such set constant at all times during the operating cycle, and to rotate at a strictly constant angular speed if the motor is connected to a constant hydraulic fluid supply. Each piston 6 effects a working and a return stroke twice in each revolution of the shaft 16.

As will emerge more fully later, each piston 6 is operative over only one-fourth of one shaft revolution. The sum of the speeds of the two pistons which are operative (i.e. travelling in a working stroke) at any one time is arranged to be constant and equal to the maximum speed attained by any single piston at any moment in the operating cycle.

This condition is satisfied when the pistons operative pair of move at speeds which vary linearly from a minimum to a max imum value in opposite phase, as shown in the diagram of FIG. 5. This diagram shows the instantaneous speeds V V respectively of the pistons of one said pair. The sum Vm, of the speeds V V remains constant with time (or angle or rotation traversed by the shaft) and is proportional to the resultant rate of volume sweeping of the two pistons. Zero speed is shown as V Negative speed, i.e. speed on the return stroke, is shown fragmcntarily in dash lines below the base line.

FIG. 6 is a diagrammatic developed view of one lobe 8 the profile of the cam 15, showing the lift provided by each identiv cal lobe, the angular extent of each lobe being I80".

Each cam lobe, which has two symmetrical halves, may be regarded as being divided into a number of sections, indicated by broken lines. Over each section at which the piston speeds V and V of the pair of pistons which at the moment are travelling on a working stroke vary linearly, as indicated in FIG. 5, the profile of the cam is parabolic, the configuration of each parabolic section being expressed by the general quadratic equation:

y=ax". where xand yare the cartesian coordinates, of a point on the cam periphery, and a is a constant determined by the depth of the cam profile.

In order to improve the distribution of hydraulic fluid between the cylinders, the individual parabolic sections of each cam lobe merge smoothly at the maximum and minimum radii of the lobe through sections of circular profile which correspond to zero piston speed. In the embodiment shown, each circular section has an angular extent of about 8 of the cam profile.

In addition, and in order to ensure the constant resultant sweeping speed Vm referred to, the individual parabolic sections are separated in the regions of maximum cam slope centrally of each flank of the cam lobe by Archimedian spiral sections corresponding to maximum piston speed. These sections extend in each case over about 8 of the cam profile.

The parabolic, spiral and circular sections of the cam profile referred to are shown in development in FIG. 6. In this figure, which relates to a single cam lobe, that is, 180 of the cam profile, P P P and P, denote the parabolic sections extending over the angular widths 4-4l, 49-86, 94 1 3| ,l39l76 R, and R denote the spiral sections (seen in development as sloping rectilinear sections), over which the parabolic sections merge into each other, extending over the angular widths 4I49, l3] 139; r r r., denote the interconnecting circular sections (seen in development as horizontal rectilinear sections), extending over the angular widths of O4 8690 90--94and l76-- 180 respectively, the sections r, and r r merging smoothly with each other. It will therefore be clear from FIG. 6 that each cam lobe is divided symmetrically into two portions, each portion comprising'successively in profile a first circular section, a first parabolic section, a spiral section, a second parabolic section and a second circular section.

The second cam lobe cooperating with the remaining four pistons is symmetrical to that illustrated in FIG. 5, so that the two lobes extend over the full 360 of the cam periphery.

The delivery of hydraulic fluid to each cylinder is controlled by the piston in an adjacent cylinder; each piston acts as a slide valve for controlling the fluid supply to an adjacent cylinder and determines the portion of the cycle over which the latter operates. This mode of distribution of the hydraulic fluid is known in the art.

The annular member 4 of the motor body is formed throughout its circumference with a pair of conduits 25, 26 communicating directly with the tangential conduits l2, 14 described above, and acting respectively as pressure fluid supply and pressure fluid outlet lines when it is desired to produce counterclockwise rotation of the shaft 16 as seen in FIG. 4: for the reverse direction of rotation the pressure fluid connections to the conduits 25 and 26 are reversed. The motor is therefore fully reversible, its speed being variable over a continuous range from zero to maximum speed identically in both directions of rotation.

A further series of conduits FIG. 4 which will be referred to hereafter as the pilot conduits is formed in the annular member 4. The conduits 27 connects the tangential conduit 13 in each cylinder with the tangential conduit 11 in the next adjacent cylinder (in a clockwise direction) so that each piston on its ascending and descending stroke connects said adjacent cylinder alternatively with the pressure fluid supply conduit 25 or outlet conduit 26. I

By numbering the consecutive pistons and cylinders I, II, III, VIII in a clockwise direction as shown in FIG. 4, the operation of the motor for a counterclockwise rotation of the shaft 16 may be described as follows:

At its bottom dead center point, contacting the circular section r of the cam profile, the piston l, acting through its tan gential conduits 13' and 14' and the pilot conduit 27, connects the space above the piston in the adjacent cylinder II with the outlet conduit 26. The piston ll thus discharges fluid to the outlet 26 and moves radially outwardly on its return stroke. The piston II closes its own tangential conduits i2" and 14", thereby cutting off the supply conduit 25 and the outlet conduit 26 from the tangential conduit 13" of the cylinder ll. Consequently, there is no flow in either direction through the pilot conduit 27 linking the conduit 13" to the conduit 11' of the adjacent cylinder III, so that there is no flow between the cylinders II and III.

Since the piston III, being spaced at from the piston I, is at the top dead center point ofits stroke, contacting the circular profile section r of the cam, it establishes communication between its own tangential conduits 12' and 13' Hydraulic fluid pressure is thus supplied through the said tangential conduit 12' of the cylinder III, the pilot conduit 27 and tangential conduit 11 to the top of the cylinder IV, above the respective piston IV, urging the latter radially inwardly on a working stroke in the cylinder IV.

The description given in respect of cylinders I, II, III and IV is sequentially repeated in respect of cylinders V, VI, VII and VIII.

The piston VIII controls the first cylinder I and, in the position shown in FIG. 4, it is at the position R of the cam, and closes its tangential conduits 12" and 14, cutting off the pilot conduit 27 and preventing communication of cylinder I with either the supply conduit 25 or the outlet conduit 26.

During the above-described part of the cycle the two operative or working pistons are pistons IV and VIII which generate the driving torque, the value of which depends upon the feed pressure of the hydraulic fluid. As the rotation of the motor proceeds, each of the diametrically-opposed pairs of pistons in turn become the operative or working pistons.

By interchanging the supply and outlet conduits 25, 26, by means for example of an electrically'operated valve, the direction of rotation of the motor shaft 16 can be reversed.

Iclaim:

l. A hydraulic motor comprising:

a. a rotatable drive shaft.

b. a central cam secured to the drive shaft.

c. two sets of cylinders extending radially with respect to the drive shaft, each set comprising four cylinders, the cylinders of the two sets being arranged symmetrically around the drive shaft,

d. a piston arranged for axial sliding movement within each cylinder and cooperating with the cam,

e, hydraulic fluid inlet and outlet ports in the cylinders, hydraulic pilot means in each cylinder including a pilot port and a pilot conduit interconnecting the pilot port and the space above the piston in an adjacent cylinder, the piston in each cylinder acting as a slide value and sequentially closing the pilot port and connecting the pilot port to the inlet and outlet ports in the cylinder to control the flow of fluid to and from the adjacent cylinder;

the cam having two lobes, each lobe being divided symmetrically into two portions and each portion comprising successively in profile a first circular section, a first parabolic section, a spiral section, a second parabolic section, and a second circular section, whereby at any mo ment in an operating cycle of the motor, the combined instantaneous speeds and hydraulic fluid flow rates of all pistons travelling on a working stroke are constant and equal respectively to the maximum piston speed and maximum flow rate attained in any cylinder during the operating cycle.

2. Hydraulic motor as claimed in claim 1, wherein each first and second parabolic profile section extends over an angular width of 37 3. Hydraulic motor as claimed in claim 1, wherein each first and second circular profile sections extend over an angular width of 4 4. Hydraulic motor as claimed in claim 1, wherein each said spiral profile section extends over an angular width of 8 5. A hydraulic machine comprising:

a, a rotatable drive shaft;

b. a number of sets of cylinders extending radially with respect to the drive shaft, each set comprising four cylinders;

c. hydraulic fluid inlet and outlet ports in each cylinder,

d. a piston arranged for axial sliding movement within each cylinder, hydraulic pilot means in each cylinder including a pilot port and a pilot conduit interconnecting the pilot port and the space above the piston in an adjacent cylinder, the piston in each cylinderacting as a slide value and sequentially closing the pilot port and connecting the pilot port to the inlet and outlet ports in the cylinder to control the flow of fluid to and from the adjacent cylinder;

e. a cam secured for rotation about the drive shaft axis relatively to the cylinders and having a number of lobes equal to the number of sets of cylinders, each lobe being similar to the others and being divided symmetrically into two portions that each comprise successively in profile a first circular section, a first parabolic section, a spiral section, a second parabolic section, and a second circular section, whereby at any moment in an operating cycle of the machine, the combine instantaneous speeds and hydraulic fluid flow rates of all pistons travelling on a working stroke are constant and equal respectively to the maximum piston speed and maximum flow rate attained in any cylinder during the operating cycle. 

1. A hydraulic motor comprising: a. a rotatable drive shaft, b. a central cam secured to the drive shaft, c. two sets of cylinders extending radially with respect to the drive shaft, each set comprising four cylinders, the cylinders of the two sets being arranged symmetrically around the drive shaft, d. a piston arranged for axial sliding movement within each cylinder and cooperating with the cam, e. hydraulic fluid inlet and outlet ports in the cylinders, hydraulic pilot means in each cylinder including a pilot port and a pilot conduit interconnecting the pilot port and the space above the piston in an adjacent cylinder, the piston in each cylinder acting as a slide value and sequentially closing the pilot port and connecting the pilot port to the inlet and outlet ports in the cylinder to control the flow of fluid to and from the adjacent cylinder; f. the cam having two lobes, each lobe being divided symmetrically into two portions and each portion comprising successively in profile a first circular section, a first parabolic section, a spiral section, a second parabolic section, and a second circular section, whereby at any moment in an operating cycle of the motor, the combined instantaneous speeds and hydraulic fluid flow rates of all pistons travelling on a working stroke are constant and equal respectively to the maximum piston speed and maximum flow rate attained in any cylinder during the operating cycle.
 2. Hydraulic motor as claimed in claim 1, wherein each first and second parabolic profile section extends over an angular width of 37* .
 3. Hydraulic motor as claimed in claim 1, wherein each first and second circular profile sections extend over an angular width of 4* .
 4. HyDraulic motor as claimed in claim 1, wherein each said spiral profile section extends over an angular width of 8* .
 5. A hydraulic machine comprising: a. a rotatable drive shaft; b. a number of sets of cylinders extending radially with respect to the drive shaft, each set comprising four cylinders; c. hydraulic fluid inlet and outlet ports in each cylinder, d. a piston arranged for axial sliding movement within each cylinder, hydraulic pilot means in each cylinder including a pilot port and a pilot conduit interconnecting the pilot port and the space above the piston in an adjacent cylinder, the piston in each cylinder acting as a slide value and sequentially closing the pilot port and connecting the pilot port to the inlet and outlet ports in the cylinder to control the flow of fluid to and from the adjacent cylinder; e. a cam secured for rotation about the drive shaft axis relatively to the cylinders and having a number of lobes equal to the number of sets of cylinders, each lobe being similar to the others and being divided symmetrically into two portions that each comprise successively in profile a first circular section, a first parabolic section, a spiral section, a second parabolic section, and a second circular section, whereby at any moment in an operating cycle of the machine, the combine instantaneous speeds and hydraulic fluid flow rates of all pistons travelling on a working stroke are constant and equal respectively to the maximum piston speed and maximum flow rate attained in any cylinder during the operating cycle. 